Flow-through photo-chemical reactor

ABSTRACT

A flow-through photochemical reactor includes a reactor body, that circumscribes a longitudinally extending channel having a generally annular cross section. This channel accommodates fluids passing between an inner wall of the reactor body and an outer wall of a photon-transmitting tube that is housed internally thereof. In addition, the reactor includes mechanically static, fluid-dynamic elements for passively inducing substantial turbulent flow within a fluid as it passes through the channel. This arrangement substantially increases the uniformity of the fluid&#39;s exposure to photons radiating from a source within the tube into the fluid as it is conducted through the channel.

This application is a continuation of application Ser. No. 08/438,234,filed May 9, 1995 now U.S. Pat. No. 5,696,380.

FIELD OF THE INVENTION

The present invention relates to photo-chemical reactors, and especiallyto flow-through chemical reactors that are particularly useful infacilitating photo-chemical reactions for "optically dense" fluidsubstrates.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,998,477--dated Dec. 21, 1976, discloses a device fornon-rigid connection of two rigid cylindrical pipes, which comprise thecombined use of flexible double lipped gaskets and toroid flexiblegaskets surrounding a bulb-shaped zone formed in one of the pipes. Thedevice is. particularly useful for fastening fragile tubes containinglight emitters to metal reactors used for photochemical processes.

U.S. Pat. No. 4,002,918--dated Jan. 11, 1977, discloses an apparatus forthe irradiation of fluids in which the fluid is conducted along thewalls of a container having walls which are permeable for the radiationto which the fluid is exposed. Radiation sources are arranged around thecontainer and an active rotor is disposed within the container. Therotor consists of a body having axial bores and pins movably disposed inthe bores and adapted to engage with their front ends the containerwalls thereby to wipe any deposits from the container walls duringrotation of the rotor.

U.S. Pat. No. 4,317,041--dated Feb. 23, 1982, discloses variousembodiments of photo-reactors in which there are at least two radiationchambers with a window arranged therebetween. UV radiation is introducedinto one of the chambers at a side opposite the window so that it passesthrough that chamber, through the window and into the other chamber. Thefluid medium to be purified is passed through the chambers and subjectedto the radiation while in the chambers, The flow of the medium isthrough the chambers in series in some embodiments and in parallel inothers. An embodiment is disclosed wherein a recirculation line isestablished around the reactor with the recirculation being continuousor intermittent. When intermittent the purified fluid medium also isdrawn off intermittently, between the periods of recirculation. In someembodiments, the amount of radiation traversing all the chambers ismonitored. If the monitored amount drops below a given amount, theapparatus is shut down. Alteratively, the rate of flow of the medium isadjusted, based on that monitored amount, with the rate of flowincreasing or decreasing, respectively, in response to increases ordecreases in that amount.

U.S. Pat. No. 4,476,105--dated Oct. 9, 1984, relates to a process forproducing gaseous hydrogen and oxygen from water. The process isconducted in a photolytic reactor which contains a water-suspension of aphotoactive material containing a hydrogen-liberating catalyst. Thereactor also includes a column for receiving gaseous hydrogen and oxygenevolved from the liquid phase. To avoid oxygen-inactivation of thecatalyst, the reactor is evacuated continuously by an external pumpwhich circulates the evolved gases through means for selectivelyrecovering hydrogen therefrom. The pump also cools the reactor byevaporating water from the liquid phase. Preferably, product recovery iseffected by selectively diffusing the hydrogen through a heatedsemipermeable membrane, while maintaining across the membrane a magneticfield gradient which biases the oxygen away from the heated membrane.This promotes separation minimizes the back-reaction of hydrogen andoxygen, and protects the membrane.

U.S. Pat. No. 5,126,111--dated Jun. 30, 1992, discloses a method ofremoving, reducing or detoxifying organic pollutants from a fluid, wateror air, by contacting the fluid with a photoreactive metal semiconductormaterial in the presence of ultraviolet light of a wavelength toactivate the photoreactive material. This is improved by simultaneouslycontacting the photoreactive material with a substance that acceptselectrons and thus inhibits hole-electron recombination. Such substancewill be such as to readily accept electrons either from the conductionbard or from superoxide ions, and to rapidly dissociate into harmlessproducts.

Still other photoreactors are described in U.S. Pat. Nos. 3,567,921;3,769,517; 3,924,246; 4,296,066; 4,381,978; 4,454,835; 4,488,935;4,544,470; 4,774,026; 4,863,608; 4,868,127; 4,957,773; 5,045,288;5,094,815; and 5,149,377.

SUMMARY OF THE INVENTION

In the context of the present invention, "static mixing" and meanstherefor relate generally to mechanically passive mixing devices, whosemixing function is driven by fluid passage past stationary, fluidredirecting elements.

Broadly speaking, the present invention relates to a flow-throughphotochemical reactor comprising a fluid conducting channel. Moreparticularly, the reactor includes a photon-transparent wall foradmitting photons into the channel. The reactor further includesinternally housed, static fluid-dynamic-effector means for passivelyinducing substantial transverse (ie radial) mixing flow within a fluidduring its longitudinal transit through the channel. This substantiallyincreases the uniformity of the fluid's exposure to photons radiatingthrough the wall and into the channel.

The foregoing embraces within its broad scope, embodiments in which aphoton-transparent tubular reactor, (with the mechanically static,fluid-dynamic effector elements disposed internally thereof), with thelight sources arranged externally of the channel, as for example, in aradial array around the tube's exterior. To make most efficientadvantage of the photons emitted from a light source, however, it ispreferred that the light source be located within the channel so thatphotons that radiate outwardly therefrom are made directly available forreaction in the surrounding fluid flow.

In accordance therefore with a more specific aspect of the presentinvention, there is provided a flow-through photochemical reactor whichincludes a reactor body, circumscribing a longitudinally extendingchannel having a generally annular cross section. The channelaccommodates the passage between an inner wall of the reactor body andan outer wall of a photon transmitting tube. The tube is housedinternally of the reactor, and is preferably arranged in co-axialalignment (ie longitudinally centered, concentric relation) relative tothe inner wall of the reactor.

This preferred reactor according to the present invention (as well asthe others that are more generically described hereinbefore) includes anarrangement of mechanically static, fluid-dynamic elements. These"operate" by passively inducing or effecting a substantial turbulentflow within the fluid as it passes through the annular channel (in thecase of the preferred embodiment), and this action substantiallyincreases the uniformity of the fluid's exposure to photons radiating,from a source within that tube, into the fluid as it is conductedthrough the channel. Note too that mechanically-static elements, whichcan be advantageously employed in the present invention, would includethose which can be manufactured from "transparent" materials.

Static effector elements suitable for use in the present invention areknown in the mixing arts--where they are referred to as static mixers.Not all such will be entirely suitable for use in every embodiment ofthe present invention. Exemplary forms of such mixers are disclosed in avariety of US patents, and elsewhere, and while not everyone is best oreven equally suited to the present application, they each disruptstreamline flow and to that extent are potentially relevant to thepresent combination. Note, however, that the benefit of the present"static effector" (that is as employed in the context of thecombinations according to the present invention as contemplated herein)is directly tied to the efficacy with which it circulates flow to (andaway) from the surface(s) through which the photons are transmitted. Themost efficacious flow pattern is one in which photon-exposed fluid isdisplaced or replaced by fluid that is either unexposed or less exposedthan the fluid that it displaces or replaces in proximity to thephoton-transmitting surface(s) Given the economic (and hence industrial)advantages that attend in-line, longitudinal flow processes, theefficacy of a given static effector in especially preferred embodimentsof the present invention is directly related to the degree to which aparticular effector directs and redirects transverse (ie relative to theoverall longitudinal flow of the fluid) flow toward thephoton-transmitting surface(s) of the reactor.

By way of example, there is disclosed in U.S. Pat. No. 3,051,453 abaffle system which divides a main stream containing substances to beblended into a number of branches or portions of streams much in themanner of a family tree, displacing one partial stream with respect toadjacent partial streams while changing the cross-sectional shapethereof, and combining the partial streams in groups corresponding tothe original dividing factor.

U.S. Pat. No. 3,620,506 discloses a fluid mixing apparatus whichincludes a plurality of stationary mixing units, formed of planarmembers, disposed in series longitudinally of a passage for sequentiallyand repeatedly dividing and recombining fluid flows during the travelthereof through the passage, with the fluid flows being directed alongdifferent serpentine paths after each division thereof.

U.S. Pat. No. 3,652,061, relates to a static element mixing tube thatemploys opposed, angularly disposed baffles which provided mixing actionby re-positioning of the stream. Mixing action at flow rates belowturbulent level is generally independent of throughput.

U.S. Pat. No. 3,733,057, deals with an in-line spiral mixer that ischaracterized by successive left and right hand spaced spiral vanesdisposed within a cylindrical tube. Each of the vanes comprises at leasttwo separate parts with a central opening therebetween. The leading edgeof each part is tapered from the outer to inner ends in the direction offluid flow to minimize accumulation of material on the edge, whichprovides a self-cleaning action.

U.S. Pat. No. 4,034,965, concerns an apparatus for mixing ordistributing a material or materials having no moving parts in which oneor more elements are fitted into a conduit. Substantial radialdisplacement of material flowing in the conduit is achieved over a shortdistance with a minimum pressure drop. Each element initially imparts arotational vector to the material stream and then transforms therotational vector to a lateral or radial vector.

U.S. Pat. No. 4,179,222, relates to a device for generating specialturbulence patterns in fluids flowing in pipes, such as for mixing,promoting chemical reactions, or accelerating the transfer of heat to orfrom the fluid through the pipe wall. Two or more sets of flow dividersare mounted in the pipe, each set including a first and second flowdivider with septum panel elements that overlap longitudinally of thepipe. The first flow divider septum elements mutually diverge downstreamin a deflected longitudinal plane in longitudinally overlappingrelationship with septum elements of the second flow divider mutuallydiverging upstream in a differing longitudinal plane so as to divert thefluid in such manner that the flow regions adjoining the pipe wall arecaused to exchange positions with flow regions in the vicinity of thepipe axis. By reversing the relative incline angles of the septumelements of corresponding flow dividers of successive sets alternatelywhen a succession of two or more sets are installed in direct series,the desired effects are augmented.

U.S. Pat. No. 4,314,974, relates to a liquid-liquid solvent extractionsystem, but discloses a static mixer--See, for example, FIG. 2 thereof.

U.S. Pat. No. 4,497,753 discloses a packing structure, for mixing or forexchange processes, in which there are at least two zig-zag layers, oneof which has a number of parallel rows of substantially rectangulardeflecting surfaces with alternating gaps in the inclined flanks.Bridges connect the rows of deflecting surfaces and are disposed in thetroughs and at the apices of the corrugated layer.

U.S. Pat. No. 4,498,786, pertains to a method and a device for mixing atleast two individual streams having different variables. In order toprovide a low-loss effective mixing within a short flow section, atleast one eddy impulse is producing the cross section of flow of atleast one individual stream. This impulse spreads out downstream,transverse to the direction of flow, to form a discrete eddy systemwhose components transverse to the main direction of flow overlap intothe other flow cross section of the other individual stream. This eddyimpulse can be produced either by at least one curved surface or by atleast one edge of a surface or of a body, but preferably by two burble(flow break-away) edges of a delta-shaped insert element which extend atan acute angle to each other.

U.S. Pat. No. 4,747,697, relates to a motionless fluid mixer for mixingtwo or more kinds of fluids, and has an elongated tubular casing intowhich a mixing element and a spacer are arranged in combination. Themixing element is provided with a helically twisted blade member.

These above exemplified static mixing devices, however, all presupposeapplications in which the fluid conducting channel is a simple (andusually cylindrical) pipe structure. These would be suitable, withoutalteration, to such applications, but are not be so readily fitted to,or efficacious in, applications such as the preferred embodiment of thepresent invention that was introduced hereinabove, in which the lightsource resides in a tube laying concentrically within the "pipe."Nevertheless, they are exemplary of the state of the static mixing arts,and in the hands of persons skilled in the static mixing art, when takenin light of the teachings herein contained, provide sufficient basis foreffecting at least some measure of the benefit associated with thepresent invention. Other static mixing elements, however, lendthemselves more readily to use in the combination according to thepreferred practice under the present invention. By way of example, theseinclude various of the elements as disclosed in U.S. Pat. Nos.3,337,194; 4,072,296; 4,093,188; 4,352,378; and 4,600,544.

Above-listed U.S. Pat. No. 3,337,194--dated Aug. 22, 1967, discloses anin-line blender for particulate materials, comprising in combination anelongated chamber having provided therein a plurality of baffle meanseach so adapted as to partially traverse said chamber therebyobstructing the path flow of solids at one or more points within saidchamber.

Above-listed U.S. Pat. No. 4,072,296--dated Feb. 7, 1978, relates to amotionless mixer including a number of baffles attached to a central rodwhich is slidably mountable within a hollow cylindrical conduit, Across-member is attached across the interior of the conduit and isconfigured to mate with a slot formed in the downstream end of thecentral rod, to prevent longitudinal motion or rotation of the mixerwithin the conduit.

Above-listed U.S. Pat. No. 4,093,188--dated Jun. 6, 1978, concerns theblending of two or more viscous fluids with a static mixer whichcomprises two or more banks of stationary baffles arranged around anaxis parallel to the overall direction of flow of the fluids to bemixed. The baffles in each bank of the element are inclined at an angleto the overall flow axis and at an angle to the baffles of adjacentbanks so that fluid streams are guided through windows or aperturesformed by abutting baffles along the interface between adjacent banks.

Above-listed U.S. Pat. No. 4,352,378--dated Oct. 5, 1982, in which aribbed construction, assembled from sheet metal bands for improved heattransfer, is built into the pipes of heat exchangers, to improve theheat exchange efficiency.

Above-listed U.S. Pat. No. 4,600,544--dated Jul. 15, 1986, relates to apacking unit having a set of deflectors within a cage for deflectingwhich of two fluids moving through the unit. The deflectors are arrangedso that in any image of the unit formed by parallel rays projected ontoa plane, regardless of how the unit is oriented with respect to theplane, at least half of the area enclosed by the perimeter of the imagewill be a shaded area, no more than 35 percent of the shaded area beingproduced by surfaces of the deflectors oriented at more than 60 degreesto the rays.

Moreover, in at least the case exemplified by the currently preferredembodiment of the present invention, there is some preliminarysuggestion that the efficacy with which turbulent flow is induced mayactually be inherently improved somewhat in an annular channel, as hasbeen suggested may be the case in relation to certain embodiments of thepresent invention which employ the static fluid flow mixing apparatus ofU.S. Pat. No. 4,929,088--dated May 29, 1990, and 4,981,368--Smith,(dated Jan. 1, 1991). The apparatus disclosed and illustrated in U.S.Pat. No. 4,929,088--Smith, (dated Mar. 29, 1990), is useful as acomponent of the present invention, and the disclosure of that patent ishereby expressly incorporated herein, in its entirety. Similarly, themethod described in U.S. Pat. No. 4,981,368--Smith, (dated Jan. 1,1991), is also hereby expressly incorporated herein, in its entirety.

In accordance with the present invention, therefore, there is provided aparticularly preferred embodiment, in which a central elongatedphoto-source is deployed within the static mixer conduit, in a centralregion of otherwise reduced mixing. Such a region, for example, tends toexist between diametrically-opposed, radially-convergent, cross-streammixing flows within that conduit. In any case, this centrally-locatedbody occupies is a zone in which there would otherwise be a reducedcross-flow. The presence of this central photo source results in thefluid flowing past it tending to be more efficiently mixed--in thatthere is less of a tendency for an unmixed "channel" of longitudinalfluid flow to establish itself within the center of the conduit. More tothe point, however, the exposure to the substrate of an optically densefluid substrate is facilitated by ensuring that the substrate uniformlypasses into the region around the photosource, in which aphoto-chemically active dose of photon energy penetrates. Thus, theouter wall of the photosource, which is preferably a photon transmittingtube, forms the inner boundary surface of the conduit.

In an especially preferred embodiment according to the presentinvention, there is provided a static mixer conduit in which tabs areeach arranged with respective edge (preferably leading upstream)adjacent to the conduit wall, and respective opposed edges (preferablytrailing downstream) that are spaced radially inwardly from the conduitwall. These tabs are operable as fluid foils which, with fluid flowingthrough the mixer, have greater fluid pressures manifest against theirupstream faces and reduced fluid pressures against their downstreamfaces. This pressure difference in the fluid adjacent to the respectivethe mutually opposed faces of each of the tabs then causes thelongitudinal flow over and past each tab to be redirected, therebyresulting in the addition of a radial cross-flow component to thelongitudinal flow of fluid through the conduit.

The present invention further includes an improved method, in which thestatic mixing is performed over a longitudinal extent of a mixing volumehaving an annular cross section. More specifically, the method of thepresent invention relates to cross-stream mixing in a fluid flow, inwhich tabs mentioned herein, redirect a longitudinal fluid flow from anouter, fluid containment boundary surface, across an intervening spacehiving an annular cross section towards an inner boundary surface.Preferably, the tabs are ramped and arranged in the fluid to flowbetween the respective boundary surfaces, to cause the fluid to flowover the edges of each such tab to deflect the generally longitudinalfluid flow inwardly from the fluid containment boundary surface, acrossthe intervening space (having the aforesaid annular cross section),towards an inner boundary surface. The inner boundary surface defines avolume which, but for the presence of that surface, would permit passageof a central longitudinal flow of non-uniform fluid mixing.

In a particularly preferred form the fluid flow over the edges of eachtab results in the flow being deflected inward and up the inclinedsurface Of the tab to generate a pair of tip vortices in the fluid flowpast each tab. The vortices of each such pair have mutually opposedrotations, about an axis of rotation oriented generally along thelongitudinal streamwise fluid flow direction, along the annular spacebetween the two boundary surfaces.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Introduction to the Drawings

FIG. 1 is an elevated, longitudinal cross section through a static mixeraccording to the combination of the present invention;

FIG. 2 is an elevated, transverse cross section taken through line 2--2of the mixer depicted in FIG. 1;

FIG. 3 is a reproduction of the view illustrated in FIG. 2, but furtherincluding representative fluid stream lines, to illustrate radialcross-flow patterns;

FIG. 4 is a cut-away perspective view illustrating vortex flowdownstream of a single, representative tab; and,

FIG. 5 is a photo reactor according to the present invention, includingthe features illustrated in the preceding Figures.

Referring now to FIGS. 1, 2 and 3, there is illustrated an embodimentaccording to the present invention, in which a static mixer 1, includesa series of tabs 2 that are secured to the side walls 3 of a conduit 4.A central photo source (eg a light source) 5 is arranged in coaxiallyaligned relation, centrally within the interior of conduit 4, where itoccupies a region of inefficient mixing.

In the illustrated embodiment, that region forms between diametricallyopposed, radially convergent, cross-stream mixing flows (see FIG. 3, inparticular) within conduit.

Static mixer 1 comprises conduit 4, in which tabs 2 are each arrangedwith respective, (leading, upstream) edges 6 adjacent the conduit wall,and respective, (trailing, downstream) opposed edges 7 that are spacedradially inwardly from the conduit wall 3. Tabs 2 operate as fluid foilswhich, with fluid flowing through the mixer, have greater fluidpressures manifest against their upstream faces 8 (see FIG. 1) andreduced fluid pressures against their downstream faces 9 (see FIG. 1).This pressure difference in the fluid adjacent to the respectivemutually opposed faces of each of the tabs then causes the longitudinalflow over and past each tab to be redirected (as is illustrated by thevarious flow streamlines that are shown in the various figures), therebyresulting in the addition of a radial cross-flow component to thelongitudinal flow of fluid through the conduit 4.

With phototube 5 occupying the zone of relatively poor mixing asdescribed above, the fluid itself is precluded from forming eddies inthat zone, in which the fluid would not be as thoroughly admixed withthe balance of the fluid flow. In this relationship, the photochemicalefficacy of the treatment can, in the hands of a person skilled in theart and in light of the teachings herein contained, be efficaciouslymanaged.

Moreover, in operation, the photochemical reactor according to thepresent invention is performed over a longitudinal extent of a mixingvolume having an annular cross-section, located between the photonsource 5 and side walls 3 of conduit 4. More specifically, there iscross-stream mixing in the longitudinal fluid flow through the presentapparatus, in which tabs 2 redirect a longitudinal fluid flow from theouter, fluid containment boundary surface of side walls 3, across anintervening space having an annular cross section towards the innerboundary surface defining the outermost extent of photon source 5.Preferably, tabs 2 are ramped and arranged in the fluid flow between therespective boundary surfaces of side walls 3 and central photon source5, to cause the fluid to flow over the edges of each tab 2 to deflectthe generally longitudinal fluid flow radially inwardly from the fluidcontainment boundary surface of side wall 3, across the interveningspace (having the aforesaid annular cross section), towards an innerboundary surface defined by the outermost surface of central body 5. Theinner boundary surface of photon source 5 circumscribes a volume which,but for the presence of that surface, would permit passage of a centrallongitudinal flow of substantial, relatively non-uniform mixing.

In FIG. 5, there is illustrated a longitudinal cross section along thelength of a photoreactor according to the present invention that isparticularly suited to the photochemical treatment of brewery beer wort.As described above, the photo reactor comprises a static mixer 1, thatincludes a series of tabs 2 that are secured to the side walls 3 of aconduit 4. A central photo source (eg a light source) 5 is arranged incoaxially aligned relation, centrally within the interior of conduit 4,where it occupies a region of inefficient mixing. The preferred staticmixer 1 comprises conduit 4, in which tabs 2 are each arranged withrespective (leading upstream) edges 6 adjacent to the conduit wall, andrespective (trailing downstream) opposed edges 7 that are spacedradially inwardly from the conduit wall 3. Tabs 2 operate as fluid foilswhich, with fluid flowing through the mixer, have greater fluidpressures manifest against their upstream faces 8 (see FIG. 1) andreduced fluid pressures against their downstream faces 9 (see FIG. 1).This pressure difference in the fluid adjacent to the respectivemutually opposed faces of each of the tabs then causes the longitudinalflow over and past each t:b to be redirected (as is illustrated by thevarious flow streamlines that are shown in the various figures), therebyresulting in the addition of a radial cross-flow component to thelongitudinal flow of fluid through the conduit 4. Still in relation toFIG. 5, phototube 5 occupies the zone of relatively poor mixing asdescribed above, the fluid itself is precluded from forming eddies inthat zone, in which the fluid would not be as thoroughly admixed withthe balance of the fluid flow. In this relationship, the photochemicalefficacy of the treatment can, in the hands of a person skilled in theart and in light of the teachings herein contained, be efficaciouslymanaged. Also as depicted in FIG. 5, a plug flow length of pipe 10 isprovided on the upstream side of the photo reactor to ensure that theflow through the reactor is a "plug flow," to help further ensureuniformity of photochemical treatment in the reactor.

In a particularly preferred form the fluid flow over the edges of eachtab results in the flow being deflected inward and up the inclinedsurface of the tab to generate a pair of tip vortices in the fluid flowpast each tab. The vortices of each such pair have mutually opposedrotations, about an axis of rotation oriented generally along thelongitudinal "streamwise" fluid flow direction, along the annular spacebetween the two boundary surfaces.

The present invention is particularly useful in facilitating thephotochemical treatment contemplated in copending U.S. patentapplication Ser. No. 08/208,908 filed Mar. 11, 1994, which is herebyincorporated, in its entirety, by reference.

We claim:
 1. A means for photochemically treating a fluid substrate in aphotoreactor comprising:a static mixer, said static mixer has a reactorbody with a longitudinally extending channel for mixing a volume of saidfluid substrate, said longitudinally extending channel has an annularcross section; flow-redirecting tabs having leading, upstream edges andtrailing, downstream opposed edges, said flow-redirecting tabs areramped and arranged in said longitudinally extending channel with theirleading, upstream edges adjacent the channel wall and their trailing,downstream opposed edges spaced radially inwardly from the channel wallto permit a longitudinal fluid flow between an outer fluid-containmentboundary surface and an inner boundary surface, said flow-redirectingtabs:(i) provide radial cross-stream mixing in said longitudinal fluidflow; (ii) redirect said longitudinal fluid flow from said outerfluid-containment boundary surface across an intervening annular spacehaving an annular cross section and towards said inner boundary surface;(iii) cause said fluid substrate to flow over edges of each said tabs todeflect said longitudinal fluid flow inwardly from saidfluid-containment boundary surface, across said intervening annularspace, and towards said inner boundary surface; and an inclined surfaceon each of said flow-redirecting tabs, said inclined surface deflectssaid fluid substrate over said edges of each said flow-redirecting tabsinwardly and upwardly along said inclined surface thereby generating apair of tip vortices in said longitudinal fluid flow past eachflow-redirecting tab, each vortex of each said pair of tip vortices ismutually opposed in rotation about an axis of rotation oriented alongsaid longitudinal fluid flow and along said intervening annular spacebetween said outer fluid-containment boundary surface and said innerboundary surface, wherein said inner boundary surface is the outer wallof a photon transmitting tube housed internally of the reactor andarranged in coaxial alignment relative to the outer fluid-containmentboundary surface of the reactor.
 2. The means for photochemicallytreating a fluid substrate in a photoreactor of claim 1 wherein saidflow-redirecting tabs are transparent.
 3. A method for photochemicallytreating a fluid substrate in a photoreactor comprising:static mixing avolume of said fluid substrate in a longitudinally extending channel ofsaid photoreactor, said longitudinally extending channel has an annularcross section wherein radial cross-stream mixing in a longitudinal fluidflow results from flow-redirecting tabs having leading, upstream edgesadjacent to the wall of said channel and trailing, downstream edgesspaced radially inwardly from said wall of said channel; redirectingsaid longitudinal fluid flow from an outer fluid-containment boundarysurface across an intervening space having an annular cross sectiontowards an inner boundary surface by said flow-redirecting tabs, saidflow-redirecting tabs being ramped and arranged in said longitudinalfluid flow between said fluid-containment boundary surface and saidinner boundary surface; causing said fluid substrate to flow over edgesof each said flow-redirecting tabs to deflect said longitudinal fluidflow inwardly from said fluid-containment boundary surface, across saidintervening annular space, and towards said inner boundary surface; anddeflecting said longitudinal fluid flow over said edges of each of saidflow-redirecting tabs inwardly and upwardly along an inclined surface ofeach of said flow-redirecting tabs thereby generating a pair of tipvortices in said longitudinal fluid flow past each of saidflow-redirecting tabs, each vortex of each said pair of tip vortices isopposed in rotation about an axis of rotation oriented along saidlongitudinal fluid flow and along said annular space between saidfluid-containment boundary surface and said inner boundary surface,wherein said inner boundary surface is the outer wall of a photontransmitting tube housed internally of the reactor and arranged inco-axial alignment relative to the outer fluid-containment boundarysurface of the reactor.